#pragma once

#include <glm/matrix.hpp>

/// https://gist.githubusercontent.com/podgorskiy/e698d18879588ada9014768e3e82a644/raw/d1f3249bf5e66023397c48c513f58e867a32e206/FrustumCull.h
class Frustum {
public:
  Frustum() {}

  // m = ProjectionMatrix * ViewMatrix
  Frustum(glm::mat4 m);

  // http://iquilezles.org/www/articles/frustumcorrect/frustumcorrect.htm
  bool IsBoxVisible(const glm::vec3& minp, const glm::vec3& maxp) const;

private:
  enum Planes {
    Left = 0,
    Right,
    Bottom,
    Top,
    Near,
    Far,
    Count,
    Combinations = Count * (Count - 1) / 2
  };

  template<Planes i, Planes j>
  struct ij2k {
    enum {
      k = i * (9 - i) / 2 + j - 1
    };
  };

  template<Planes a, Planes b, Planes c>
  glm::vec3 intersection(const glm::vec3* crosses) const;

  glm::vec4 m_planes[Count];
  glm::vec3 m_points[8];
};

inline Frustum::Frustum(glm::mat4 m) {
  m = glm::transpose(m);
  m_planes[Left] = m[3] + m[0];
  m_planes[Right] = m[3] - m[0];
  m_planes[Bottom] = m[3] + m[1];
  m_planes[Top] = m[3] - m[1];
  m_planes[Near] = m[3] + m[2];
  m_planes[Far] = m[3] - m[2];

  glm::vec3 crosses[Combinations] = {glm::cross(glm::vec3(m_planes[Left]), glm::vec3(m_planes[Right])),
                                     glm::cross(glm::vec3(m_planes[Left]), glm::vec3(m_planes[Bottom])),
                                     glm::cross(glm::vec3(m_planes[Left]), glm::vec3(m_planes[Top])),
                                     glm::cross(glm::vec3(m_planes[Left]), glm::vec3(m_planes[Near])),
                                     glm::cross(glm::vec3(m_planes[Left]), glm::vec3(m_planes[Far])),
                                     glm::cross(glm::vec3(m_planes[Right]), glm::vec3(m_planes[Bottom])),
                                     glm::cross(glm::vec3(m_planes[Right]), glm::vec3(m_planes[Top])),
                                     glm::cross(glm::vec3(m_planes[Right]), glm::vec3(m_planes[Near])),
                                     glm::cross(glm::vec3(m_planes[Right]), glm::vec3(m_planes[Far])),
                                     glm::cross(glm::vec3(m_planes[Bottom]), glm::vec3(m_planes[Top])),
                                     glm::cross(glm::vec3(m_planes[Bottom]), glm::vec3(m_planes[Near])),
                                     glm::cross(glm::vec3(m_planes[Bottom]), glm::vec3(m_planes[Far])),
                                     glm::cross(glm::vec3(m_planes[Top]), glm::vec3(m_planes[Near])),
                                     glm::cross(glm::vec3(m_planes[Top]), glm::vec3(m_planes[Far])),
                                     glm::cross(glm::vec3(m_planes[Near]), glm::vec3(m_planes[Far]))};

  m_points[0] = intersection<Left, Bottom, Near>(crosses);
  m_points[1] = intersection<Left, Top, Near>(crosses);
  m_points[2] = intersection<Right, Bottom, Near>(crosses);
  m_points[3] = intersection<Right, Top, Near>(crosses);
  m_points[4] = intersection<Left, Bottom, Far>(crosses);
  m_points[5] = intersection<Left, Top, Far>(crosses);
  m_points[6] = intersection<Right, Bottom, Far>(crosses);
  m_points[7] = intersection<Right, Top, Far>(crosses);
}

// http://iquilezles.org/www/articles/frustumcorrect/frustumcorrect.htm
inline bool Frustum::IsBoxVisible(const glm::vec3& minp, const glm::vec3& maxp) const {
  // check box outside/inside of frustum
  for (int i = 0; i < Count; i++) {
    if ((glm::dot(m_planes[i], glm::vec4(minp.x, minp.y, minp.z, 1.0f)) < 0.0) &&
        (glm::dot(m_planes[i], glm::vec4(maxp.x, minp.y, minp.z, 1.0f)) < 0.0) &&
        (glm::dot(m_planes[i], glm::vec4(minp.x, maxp.y, minp.z, 1.0f)) < 0.0) &&
        (glm::dot(m_planes[i], glm::vec4(maxp.x, maxp.y, minp.z, 1.0f)) < 0.0) &&
        (glm::dot(m_planes[i], glm::vec4(minp.x, minp.y, maxp.z, 1.0f)) < 0.0) &&
        (glm::dot(m_planes[i], glm::vec4(maxp.x, minp.y, maxp.z, 1.0f)) < 0.0) &&
        (glm::dot(m_planes[i], glm::vec4(minp.x, maxp.y, maxp.z, 1.0f)) < 0.0) &&
        (glm::dot(m_planes[i], glm::vec4(maxp.x, maxp.y, maxp.z, 1.0f)) < 0.0)) {
      return false;
    }
  }

  // check frustum outside/inside box
  int out;
  out = 0;
  for (int i = 0; i < 8; i++) out += ((m_points[i].x > maxp.x) ? 1 : 0);
  if (out == 8)
    return false;
  out = 0;
  for (int i = 0; i < 8; i++) out += ((m_points[i].x < minp.x) ? 1 : 0);
  if (out == 8)
    return false;
  out = 0;
  for (int i = 0; i < 8; i++) out += ((m_points[i].y > maxp.y) ? 1 : 0);
  if (out == 8)
    return false;
  out = 0;
  for (int i = 0; i < 8; i++) out += ((m_points[i].y < minp.y) ? 1 : 0);
  if (out == 8)
    return false;
  out = 0;
  for (int i = 0; i < 8; i++) out += ((m_points[i].z > maxp.z) ? 1 : 0);
  if (out == 8)
    return false;
  out = 0;
  for (int i = 0; i < 8; i++) out += ((m_points[i].z < minp.z) ? 1 : 0);
  if (out == 8)
    return false;

  return true;
}

template<Frustum::Planes a, Frustum::Planes b, Frustum::Planes c>
inline glm::vec3 Frustum::intersection(const glm::vec3* crosses) const {
  float D = glm::dot(glm::vec3(m_planes[a]), crosses[ij2k<b, c>::k]);
  glm::vec3 res = glm::mat3(crosses[ij2k<b, c>::k], -crosses[ij2k<a, c>::k], crosses[ij2k<a, b>::k]) *
                  glm::vec3(m_planes[a].w, m_planes[b].w, m_planes[c].w);
  return res * (-1.0f / D);
}